In general, electromagnetic interference (EMI) is electromagnetic radiation from an electrical source that interrupts the normal function of an electronic device. EMI may cause noise in signal transmission between electronic devices. Thus, there has been on-going effort in developing effective EMI reduction techniques.
Currently, there are two common approaches to reduce EMI emission. If the EMI emission is primarily being caused by poor shielding and/or grounding at interconnect interfaces (e.g., external cable connector), the interconnect interfaces may be redesigned to increase shielding and/or grounding. However, redesigning the interconnect interfaces may add considerable cost to the interconnect. Furthermore, some interconnect interface may have to conform to existing industry-wide standards. Thus, it may be difficult to redesign these interconnect interface without modifying the applicable standards.
Another conventional approach to reduce EMI emission is to use spread spectrum clocking (SSC). SSC reduces EMI emission by spreading the radiated energy over a wider frequency band. Thus, instead of maintaining a constant system frequency, SSC modulates the clock frequency along a predetermined path (also referred to as a modulation profile). However, SSC may not be appropriate for certain applications, such as applications that pertain to video and audio, because modulation of the clock frequency may cause noticeable visual or audio distortion.